Oil-Cooled Carbon Seal

ABSTRACT

A seal system has: a first member; a seal carried by the first member and having a seal face; and a second member rotatable relative to the first member about an axis. The second member has: a seat on a first piece of the second member, the seat having a seat face in sliding sealing engagement with the seal face; and a radially outwardly closed collection channel for collecting centrifuged oil; a second piece encircling and attached to the first piece and having a circumferential array of apertures; and cooperating with the first piece to define a plenum; and a flowpath from the collection channel passing radially outward axially spaced from the seat face to cool the seat face and passing axially away from the seat face in the plenum.

CROSS-REFERENCE TO RELATED APPLICATIONS

Benefit is claimed of U.S. Patent Application No. 63/125,801, filed Dec.15, 2020, by Nigel David Sawyers-Abbott et al., and entitled “Oil-CooledCarbon Seal” and this is a Continuation-in-Part of U.S. patentapplication Ser. No. 16/173,500, filed Oct. 29, 2018, by Armando Amadoret al., and entitled “Oil-Cooled Carbon Seal”, which published as U.S.Patent Application Publication No. 2020/0131936A1 on Apr. 30, 2020, thedisclosures of which applications and publication are incorporated byreference herein in their entireties as if set forth at length.

BACKGROUND

The disclosure relates to gas turbine engines. More particularly, thedisclosure relates to cooling of carbon seals in gas turbine engines.

Carbon seals are commonly used to seal between relatively rotatingcomponents in gas turbine engines. In typical situations, the annularcarbon seal is spring biased into engagement with an annular seat(typically metallic such as a steel). Often, the carbon seal is onnon-rotating static structure and the seat rotates with one of theengine shafts. The sliding engagement causes frictional heating. Theheat must be dissipated. With a rotating seat, it is common to use oilcooling. Generally, oil-cooled carbon seals are divided into twocategories: “dry face” seals wherein the oil passes through passagewaysin the seat without encountering the interface between seal face andseat face; and “wet face” seals wherein the oil passes through the seatto the interface so that the oil that flows through the seat cools theseat but then lubricates the interface to further reduce heatgeneration.

For both forms of seals, the oil may be delivered through a nozzle andslung radially outward by the rotating component and collected in aradially outwardly closed and inwardly open collection channel fromwhich the passageways extend further radially outward.

U.S. Pat. No. 4,406,459 (the '459 patent), Davis et al., Sep. 27, 1983,“Oil Weepage Return for Carbon Seal Plates” shows a seal with two setsof passageways through the seat. One set delivers oil to the interfaceas a wet face seal. Another set helps centrifugally pump out oil thathas weeped radially inward from the interface.

U.S. Pat. No. 4,928,978 (the '978 patent), Shaffer et al., May 29, 1990,“Rotating shaft seal” shows an alternative wet face seal.

United States Patent Application Publication 20180045316A1 (the '316publication), Kovacik et al., Feb. 15, 2018, “Hydrodynamic Seal SeatCooling Features” shows a dry face seal wherein the oil passageways havetwo legs: an upstream leg receiving oil from a collection notch which inturn has collected the oil from a nozzle; and a downstream leg extendingradially outward from the upstream leg generally close to and parallelto the sealing interface.

SUMMARY

One aspect of the disclosure involves a seal system comprising: a firstmember; a seal carried by the first member and having a seal face; and asecond member rotatable relative to the first member about an axis. Thesecond member has: a seat on a first piece of the second member, theseat having a seat face in sliding sealing engagement with the sealface; a radially outwardly closed collection channel for collectingcentrifuged oil; and a second piece encircling and attached to the firstpiece. The second piece has a circumferential array of apertures andcooperates with the first piece to define a plenum. A flowpath from thecollection channel passes radially outward axially spaced from the seatface to cool the seat face and passes axially away from the seat face inthe plenum.

A further embodiment of any of the foregoing embodiments mayadditionally and/or alternatively include the flowpath passing through aplurality of passageway legs in the first piece.

A further embodiment of any of the foregoing embodiments mayadditionally and/or alternatively include the flowpath passing from thepassageway legs in the first piece through an annular channel in thefirst piece and to the plenum.

A further embodiment of any of the foregoing embodiments mayadditionally and/or alternatively include the passageway legs beingfirst passageway legs, the flowpath passing from the first passagewaylegs and through respective associated second passageway legs in thefirst piece and to the plenum.

A further embodiment of any of the foregoing embodiments mayadditionally and/or alternatively include the second passageway legshaving respective spiral surface enhancements.

A further embodiment of any of the foregoing embodiments mayadditionally and/or alternatively include the second passageway legsbeing threaded.

A further embodiment of any of the foregoing embodiments mayadditionally and/or alternatively include the seal being a carbon seal.

A further embodiment of any of the foregoing embodiments mayadditionally and/or alternatively include the seat being steel and/orthe seat and seal being full annular.

further embodiment of any of the foregoing embodiments may additionallyand/or alternatively include a gas turbine engine including the sealsystem and/or wherein the second member is a shaft.

A further embodiment of any of the foregoing embodiments mayadditionally and/or alternatively include the seal system furthercomprising an oil source positioned to introduce oil to the passagewaylegs.

A further embodiment of any of the foregoing embodiments mayadditionally and/or alternatively include a method for using the sealsystem. The method comprises relatively rotating the second member tothe first member about the axis, the rotation centrifugally driving aflow of oil along the flowpath to cool the seat face.

A further embodiment of any of the foregoing embodiments mayadditionally and/or alternatively include spraying the oil from anozzle.

A further embodiment of any of the foregoing embodiments mayadditionally and/or alternatively include an oil source positioned tointroduce oil to the passageway legs.

A further embodiment of any of the foregoing embodiments mayadditionally and/or alternatively include the seal system being a dryface seal.

A further embodiment of any of the foregoing embodiments mayadditionally and/or alternatively include the sprayed oil beingcentrifugally collected in a radially outwardly closed channel fromwhich the passageway legs extend.

Another aspect of the disclosure involves a seal system comprising: afirst member comprising a seal with a seal face; and a second membercomprising a seat with a seat face and a plurality of coolingpassageways. The second member is rotatable about an axis relative tothe first member. The seal face and the seat face are in sliding sealingengagement. The cooling passageways have respective surfaceenhancements.

A further embodiment of any of the foregoing embodiments mayadditionally and/or alternatively include each cooling passagewaysurface enhancement being at least one spiral.

A further embodiment of any of the foregoing embodiments mayadditionally and/or alternatively include each cooling passagewaysurface enhancement being a thread.

A further embodiment of any of the foregoing embodiments mayadditionally and/or alternatively include: the second member furtherhaving a collection channel; and the second member further having aplurality of feed passageways, each feed passageway coupling anassociated said cooling passageway to the collection channel.

A further embodiment of any of the foregoing embodiments mayadditionally and/or alternatively include each said feed passagewaybeing positioned at an oblique angle relative to both the collectionchannel and the associated cooling passageway.

A further embodiment of any of the foregoing embodiments mayadditionally and/or alternatively include the second member beingcoupled to and configured to rotate with a rotatable shaft, and thefirst member being configured to remain stationary while the secondmember rotates with the rotatable shaft.

A further embodiment of any of the foregoing embodiments mayadditionally and/or alternatively include the seal system includingbetween 10 and 100 cooling passageways and between 10 and 100 feedpassageways.

A further embodiment of any of the foregoing embodiments mayadditionally and/or alternatively include: a distance between anoutermost edge of the grooves of the threaded passageway and the seatface being between 0.76 mm and 6.35 mm; and an angle formed between acenter axis of each cooling passageway and the seat face being greaterthan zero.

A further embodiment of any of the foregoing embodiments mayadditionally and/or alternatively include the seal system being a dryface seal and the feed passageways and cooling passageways beingconfigured to provide cooling fluid such that the cooling fluid remainsseparate from an interface where the seal face and the seat face are insliding engagement.

A further aspect of the disclosure involves a method for manufacturingthe seal system. The method comprises: forming a precursor of the secondmember; and forming of the surface enhancements by at least one oftapping and EDM.

A further embodiment of any of the foregoing embodiments mayadditionally and/or alternatively include forming precursors of thecooling passageways by drilling.

A further embodiment of any of the foregoing embodiments mayadditionally and/or alternatively include a method for using the sealsystem. The method comprises: rotating the second member about the axisrelative to the first member; the rotation driving respective flows offluid through the passageways; and the flows cooling the second member.

A further embodiment of any of the foregoing embodiments mayadditionally and/or alternatively include the surface enhancements beingspiral enhancements and the spiral enhancements inducing swirl of therespective flows in the passageways.

A further embodiment of any of the foregoing embodiments mayadditionally and/or alternatively include a gas turbine enginecomprising: an engine case, a fan, a compressor section, a turbinesection, a rotating shaft; and the seal system positioned within the gasturbine engine (e.g., within the compressor section of the gas turbineengine).

The details of one or more embodiments are set forth in the accompanyingdrawings and the description below. Other features, objects, andadvantages will be apparent from the description and drawings, and fromthe claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial partially schematic central axial sectional view ofa first seal system.

FIG. 1A is an enlarged view of a sealing interface area of the sealsystem of FIG. 1.

FIG. 2 is a partially schematic central axial sectional view of a gasturbine engine.

FIG. 3 is a partial partially schematic central axial sectional view ofa second seal system.

FIG. 3A is an enlarged view of a sealing interface area of the secondseal system of FIG. 3.

FIG. 4 is an enlarged central axial sectional view of a third sealingsystem.

FIG. 5 is an enlarged central axial sectional view of a fourth sealingsystem.

FIG. 6 is an enlarged central axial sectional view of a fifth sealingsystem.

FIG. 7 is an enlarged central axial sectional view of a sixth sealingsystem.

Like reference numbers and designations in the various drawings indicatelike elements.

DETAILED DESCRIPTION

FIG. 1 shows a seal system 100 having a first member 102 carrying a seal104. The example seal 104 is a carbon seal having a seal surface or face106. The example seal 104 is formed as a body of revolution about anaxis 500 which is an axis of relative rotation between the first member102 and a second member 110. FIG. 1 further shows an outward radialdirection 502. The example seal face 106 is a radial face. The secondmember 110 comprises a piece 112 (seat piece) forming a seat for theseal with a seat surface or face 114 in sliding sealing engagement withthe seal face 106 at a sealing interface.

The example illustrated configuration is a dry face configuration. Theseal 104 may be biased into axially compressive engagement with the seatface 114 via one or more factors including pressure bias and springloading. The seal 104 is shown as sealing a space or region 120 inboardof the sealing interface from a space or region 122 outboard. Dependingupon configuration, the pressure difference may bias the seal in eitherdirection. FIG. 1 further shows a spring 124 (e.g., a coil spring)providing the required bias. There may be a circumferential array ofsuch springs about the axis 500 each under axial compression.

In one group of examples discussed below, the second member 110 isrotating in an inertial frame of reference while the first member 102 iseither stationary or counter-rotating. The rotating of the second member110 may create a centrifugal oil flow action discussed further below.

In operation, the relative rotation produces frictional heating at thesliding interface between the faces 106 and 114. Cooling to dissipatethis heat is therefore desirable. As discussed above, it is well-knownto provide a circumferential array of oil flow passages through a seat.These are typically drilled after machining gross features of the seat.FIG. 1A, however, shows the seat piece 112 as having an annular channel130 axially spaced from the seat face 114. The example annular channelextends from a radially inboard inner diameter (ID) base 132 to aradially outboard outer diameter (OD) opening 134 in an OD surface 136of the seat piece 112. The channel 130 also has a first surface or face140 and a second surface or face 142 axially spaced therefrom. Thechannel 130 may be machined in the piece 112 by conventional methods,such as turning or milling, or advanced methods, such as EDM.

FIG. 1A further shows a circumferential array of passageway legs(passageways or feed passageways) 150 (e.g., drilled right circularcylindrical passageways) connected to the annular channel 130 atrespective first ends 152 and open to a surface portion 156 of the piece112 at their second ends 154. An example number of passageways 150 is 10to 100, more particularly 20 to 80 or 25 to 55 in seal sizes used on gasturbine engines. In operation, centrifugal action causes an accumulation160 of oil to be captured by the second member 110 in a radiallyoutwardly closed collection channel 164. The passageway second ends 154form outlets from the collection channel allowing oil flows 162 to passoutward through the passageways to the channel 130. The flows 162 fromthe individual passageways 150 merge to form a flow 165 in the channel130. The flow 165 flows radially outward to be discharged as a dischargeflow 166. The radial oil flow 165 in the channel cools the seat piece112 and, thereby, cools the seat face and seal face.

The example feed passageways 150 are shown oblique to both the axial andradial directions for reduce abrupt flow transitions (e.g., relative toan alternative where they extended axially from the collection channelwhere there would be an abrupt transition to the channel 130).

To form the channel 164, FIG. 1A shows a weir formed by an annularmember 170 accommodated partially in a radially inwardly open channel172 in the seat piece 112. A portion of the member 170 protrudesradially inwardly from an opening of the channel 172 at the surface 156.As an oil source, FIG. 1 shows an oil pump 180 delivering oil from areservoir 182 via a conduit 184. The conduit 184 may terminate at one ormore nozzles 186. Each nozzle may have a respective outlet 188discharging a spray 167 of the oil. The sprayed oil collects on asurface of the first member and is slung radially outward as a flow 168(FIG. 1) to the channel 164. Oil from the flow 166 may be collected andreturned to the reservoir 182 by a conventional collection apparatus(not shown).

FIG. 1A further shows the seat face 106 having a radial span RS₁ and thechannel 130 as having a radial span RS₂. The example radial spans areoriented so that the channel 130 fully radially overlaps the seal face106. This provides a short thermal conductive flowpath for heat to passfrom the seat face 114 to the flow 165 in the channel 130. FIG. 1Afurther shows an angle θ₁ between the seal face/seat face on the onehand and the adjacent channel face 140 on the other hand. Example θ₁ isgreater than zero. More particularly, with the seal face extendingexactly or close to exactly radially, the adjacent portion of thechannel face 140 diverges at the angle θ₁ in the radial outwarddirection. This divergence from radial helps cause the flow 165 toremain attached to the face 140. The opposite inclination wouldpotentially risk flow separation and loss of heat conduction. Exampleθ₁, however, may be fairly small in order to maintain coolingeffectiveness as the flow 165 progresses radially outward toward theouter diameter (OD) extent of the seal face. Thus, example θ₁ is0-30.0°, more particularly, 0-12.0°, 0.5-10.0°, or 1.0-10.0° or2.0-8.0°. The second face 142 may similarly diverge from the first faceat an angle θ₂. But this divergence θ₂ may represent an artifact ofmanufacturing such as from a tapered bit. Example θ₂ is 0° to 30.0°,more particularly 0° to 15.0° or 0° to 10.0° or 0° to 5.0°. Alternativelower ends on those ranges are 1.0° and 3.0°. Example span S₁ betweenthe seat face 114 and the channel face 140 is 0.030 inch to 0.250 inch(0.76 mm to 6.35 mm), more narrowly 2.0 mm to 6.0 mm or 2.5 mm to 5.0mm. Example channel width S₂ is 0.030 inch to 0.250 inch (0.76 mm to6.35 mm), more narrowly 1.0 mm to 6.0 mm or 2.0 mm to 6.0 mm or 2.5 mmto 5.0 mm.

An example member 170 may be formed by spiral winding such as used forretaining rings. Alternatively, a weir may be integrally machined intoseat piece 112.

In various implementations, the use of the annular channel 130 may haveone or more of several advantages relative to any particular baseline.For example, when contrasted with a baseline arrangement as in the '316publication, the channel 130 may provide more circumferential uniformityof cooling which may help reduce heat generation and wear. For example,discrete passages may produce a circumferential array of cool zonesinterspersed with warmer zones. The differential thermal expansion ofcool portions of the seat and hot portions of the seat may produce anuneven seat surface generating unnecessary heat and potentiallycompromising sealing.

FIG. 2 shows a turbofan engine 20 having an engine case 22 containing arotor shaft assembly 23. An example engine is a turbofan. Alternativesinclude turbojets, turboprops, turboshafts, and industrial gas turbines.The example turbofan is a two-spool turbofan. Via high 24 and low 25shaft portions of the shaft assembly 23, a high pressure turbine (HPT)section 26 and a low pressure turbine (LPT) section 27 respectivelydrive a high pressure compressor (HPC) section 28 and a low pressurecompressor (LPC) section 30. The engine extends along a longitudinalaxis (centerline) 500 from a fore end to an aft end. Adjacent the foreend, a shroud (fan case) 40 encircles a fan 42 and is supported by vanes44. An aerodynamic nacelle 41 around the fan case is shown and anaerodynamic nacelle 45 around the engine case is shown.

Although a two spool (plus fan) engine is shown, an alternativevariation involves a three spool (plus fan) engine wherein anintermediate spool comprises an intermediate pressure compressor (IPC)between the LPC and HPC and an intermediate pressure turbine (IPT)between the HPT and LPT. In another aspect a three-spool engine, the IPTdrives a low pressure compressor while the LPT drives a fan, in bothcases either directly or indirectly via a transmission mechanism, forexample a gearbox.

In the example embodiment, the low shaft portion 25 of the rotor shaftassembly 23 drives the fan 42 through a reduction transmission 46. Anexample reduction transmission is an epicyclic transmission, namely aplanetary or star gear system.

FIG. 2 also shows at their outboard ends, the vanes 44 have flanges 60bolted to an inner ring structure of the fan case to tie the outboardends of the vanes together. Integral therewith or fastened thereto is aforward mounting structure 62 (e.g., devises which form part of a fourbar mechanism) and provides forward support to the engine (e.g.,vertical and lateral support). To mount the engine to the aircraft wing,a pylon 64 is mounted to the structure 62 (e.g., forming the outer partthereof). The pylon is also mounted to a rear engine mount 66.

In one example, FIG. 2 shows a location 90 for the seal system 100wherein the first member 102 may be mounted to (or integrally formedwith) a static bearing support 80 and the second member 110 may bemounted to (or integrally formed with) a forward portion of the lowshaft 25. Alternatively, in a location 92, the first member 102 may bemounted to (or integrally formed with) a static hub 82 and the secondmember 110 mounted to (or integrally formed with) a fan shaft 81. Inthese two illustrated examples, the seal system is positioned adjacentone end of a bearing system to isolate the bearing system. Similarlocations may be provided for other bearings in the engine. For example,locations 94 and 96 may represent locations where the sealing is betweenthe high spool and static structure on either side of a bearingsupporting the high spool.

FIG. 3 shows an alternate seal system 200 configuration, otherwisesimilar to FIG. 1 with several exceptions. A first exception is that thecooling channel 130 extends radially outward to a plenum 220 (FIG. 3A).The plenum 220 is defined by the combination of: a further annularchannel in a first seat piece 212; and a second piece 222 encircling andattached to the first piece. The example second piece 222 is formed asan annular sleeve having a circumferential array of apertures 224extending between an inner diameter (ID) surface 226 and an outerdiameter (OD) surface 228. The apertures (e.g., drilled holes) formplenum outlets. The ID surface is engaged to the OD surface of the firstseat piece 212 fore and aft of the plenum 220 (e.g., via interferencefit or a braze joint). Alternative configurations may have the secondpiece 222 as nondestructively removable from the first piece such as viaa retaining clip or wire (e.g. snap ring). Similarly, in such removableconfigurations, separate seals may be provided between the pieces (e.g.,O-rings).

The apertures 224 are axially offset from the outer diameter opening ofthe channel 130 to the plenum 220. An example number of apertures 224 is10 to 100, more particularly 20 to 80 or 25 to 55 in seal sizes used ongas turbine engines. The plenum 220 and apertures 224 may provide one ormore of several functions. First, the apertures may provide a meteringfunction (metering/restricting discharge flows 266) helping ensure theflow has sufficient residence time in the channel 130 to not separatefrom the face 140 and to provide sufficient cooling. Additionally,residence time in the plenum 220 may further cool the first seat piece212 to maximize the cooling. The axial offset of the apertures 224 fromthe outlet or OD end of the channel 134 helps ensure that flow is alongthe length of the plenum 220 to again maximize cooling efficiency.Example offset S₃ (measured center-to-center) is 0.00 inches to 0.50inches (0.0 mm to 12.7 mm), more particularly, 0.00 inches to 0.30inches (0.0 mm to 7.6 mm) or, for non-zero values 0.10 inch to 0.30 inch(2.5 mm to 7.6 mm) or 0.10 inch to 0.50 inch (2.5 mm to 12.7 mm).

A further difference between the FIG. 3 and FIG. 1 systems is the FIG. 3presence of an integral weir formed in the first piece. This may be morerepresentative of conventional weirs.

The plenum 220 could be used with seats having multiple radialpassageways 300 (FIG. 4, e.g., a circumferential array of passageways)rather than a single continuous annular passageway 130. The examplepassageways 300 may be drilled circular holes. Each example passageway300 has an inlet 302 at the end 152 of a respective associated one ofthe passageways 150 (feed passageways). The inlet 302 may be at or nearan inner diameter (ID) end 304 of the passageway. The passageway has anouter diameter end 306 forming a passageway outlet. The example inlet isin a lateral surface 308 of the passageway.

Passageway radial span RS₁ and angle θ₁ may be as discussed above forthe FIGS. 1 and 3 embodiments. The passageway count may also be similar.However, it is also possible that the angle θ₁ have negative values thatactually converge toward the radial direction and face 114 in theoutward radial direction.

An example diameter of the passageways 300 may be at least 0.060 inch(0.152 centimeters). For example, it may be an example 0.060 inch (0.152centimeters) to 0.30 inch (0.762 centimeter). The diameter may be thesame or less than the diameter of the passageways 150 dependent on thecooling needs. This may allow maintenance of flow along the passageway300 surface. The larger cross-sectional area of the feed passageway 150helps provide sufficient oil. However, the further restriction providedby the plenum outlets may help maintain surface contact along the radialspan of the passageways 300. Thus, the plenum outlets 224 may be smallerin number and/or individual cross-sectional area than the passageways300. Thus, total plenum cross-sectional area may be smaller than totalpassageway 300 cross-sectional area. A proximity of the surface of thepassageway 300 to the seat face may be of similar span to that S₁ of thechannel noted above. Manufacture may be via conventional means as notedabove with drilling of the feed passageways and cooling passageways intoa cast and/or machined precursor of the seat.

Although the example FIG. 4 embodiment is based upon the FIG. 3configuration having an integral weir, alternative embodiments could bemade based upon other seat configurations including the separate weir ofFIG. 1. Similarly, the plenum 220 could be added to yet otherconfigurations of passageways. For example, they may include passagewayswith a partially tangential orientation such as those of the '316publication noted above.

However, to increase heat transfer to the flows through the passageways,the passageways may have surface-enhanced passageway cross-sections. Thesurface enhancements increase the surface area for a given passagecross-sectional area or transverse linear dimension. Examples includesplined or fluted cross-sections, and the like. Such surface-enhancedpassageways could be formed by techniques such as plungeelectrodischarge machining (EDM). Such EDM may be done after drilling apilot hole or without a pilot hole.

In addition to cylindrical surface-enhanced passageways (e.g., ridgessuch as straight splines or fluting (not shown) separated by straightgrooves or channels), other enhancements may take other forms such aspassageways 320 (FIG. 5) having a spiral enhancement 322 (ridge(s) orprojection(s)) leaving groove(s) or recess(es)/channel(s) betweenprojections or turns of a projection. The example spiral enhancement isspiral/helical splines or fluting shown with a relatively high helixangle θ₃ (a ramping helix angle vs. an off-axial helix angle of 90°-θ₃)that imparts swirl to the fluid flowing radially outward. An example ofθ₃ is broadly 20.0° to 88.0°, more narrowly 45.0° to 88.0° or 70.0° to88.0° for EDM-formed enhancements. The swirl may help keep the surfaceof the passageway 320 wetted for high heat transfer and residence timefor improved heat absorption.

Such enhancements may, for example, be made via plunge EDM (afterpre-drilling of a pilot hole or without pilot hole) with a rotation ofthe EDM electrode during the plunge. FIG. 5 shows the enhancements 322as including a plurality of alternating ridges/projections andgrooves/recesses when viewed in axial section of the passageway. Thespiral is shown schematically, particularly its intersection with thepassageway 150. An example spiral ridge/projection count per passagewayis four to twenty, more particularly four to ten. Count will generallybe geometrically related to the helix angle and projection/groove width.Example projection height (radial difference relative to passage wayaxis of projection apex and recess base) is 5.0% to 30.0% of the radiusat the groove base, more narrowly 10.0% to 25%. A proximity of thesurface of the passageway 320 to the seat face (e.g., measured from theadjacent location on the groove base) may be of similar span to that S₁of the channel noted above.

For the example surface-enhanced passageways, the passagewaycross-sectional area (or minimum passageway cross-sectional area ifthere is lengthwise/streamwise variation) may be the same in absoluteand relative terms as that noted above for the passageway 300.

Alternative spiral feature(s) include relatively low helix anglefeatures such as thread(s). FIG. 6 shows passageway 340 with such athread 342. Potential threads include single-lead threads, multiple leadthreads, and so forth. Manufacture techniques include drilling andtapping or, as noted above, EDM. Again, viewed in section, the one ormore threads appear as a series of ridges/projections andgrooves/recesses. The thread(s) may have a relatively low helix angle θ₃such as found in typical common thread forms 2.0° to 15.0° or 4.0° to12.0°. Thread height may be as described for the FIG. 5 spiralenhancement.

Example threads are coarse threads wherein the thread(s) have a largerpitch (few threads per axial distance) than fine threaded tapped holeswhich have a smaller pitch (more threads per axial distance). Relativelycoarse threads may limit stress concentrations that may otherwisecontribute to cracking. Examples of coarse threads include, but are notlimited to, ACME, worm, ball, and trapezoidal threads of sufficientlycoarse pitch to avoid stress concentrations. Particular desirablecoarseness may be determined by longevity testing such that stressfailures in the passageways do not occur over seat face lifetimes. Theoptimal form may depend on rotational speed of the shaft, radius of theseal interface, oil temperature and viscosity, and seal temperature attarget operating conditions.

Additionally, the surface enhancements may be employed in the absence ofthe plenum 220. FIG. 7 shows a passageway 360 having a spiralenhancement 362 similar to that of FIG. 6 but without a plenum.

Further manufacture variations include additive manufacture of the seat.This allows passageways such as non-straight passageways and/or complexenhancements to be formed with the surface enhancements. For example,the passageways may spiral in the circumferential direction.

Additional variations include seals where the oil is not delivered froma spray nozzle, but instead passes outward from a plenum (e.g., as inthe '459 and '978 patents above) or via other means.

Further variations include seals where cooling fluids (particularlyliquids) other than oil are used.

The use of “first”, “second”, and the like in the following claims isfor differentiation within the claim only and does not necessarilyindicate relative or absolute importance or temporal order. Similarly,the identification in a claim of one element as “first” (or the like)does not preclude such “first” element from identifying an element thatis referred to as “second” (or the like) in another claim or in thedescription.

Where a measure is given in English units followed by a parentheticalcontaining SI or other units, the parenthetical's units are a conversionand should not imply a degree of precision not found in the Englishunits.

One or more embodiments have been described. Nevertheless, it will beunderstood that various modifications may be made. For example, whenapplied to an existing baseline seal or machine configuration, detailsof such baseline may influence details of particular implementations.Accordingly, other embodiments are within the scope of the followingclaims.

What is claimed is:
 1. A seal system comprising: a first member; a sealcarried by the first member and having a seal face; and a second memberrotatable relative to the first member about an axis and having: a seaton a first piece of the second member, the seat having a seat face insliding sealing engagement with the seal face; and a radially outwardlyclosed collection channel for collecting centrifuged oil; a second pieceencircling and attached to the first piece and: having a circumferentialarray of apertures; and cooperating with the first piece to define aplenum; and a flowpath from the collection channel passing radiallyoutward axially spaced from the seat face to cool the seat face andpassing axially away from the seat face in the plenum.
 2. The sealsystem of claim 1 wherein: the flowpath passes through a plurality ofpassageway legs in the first piece.
 3. The seal system of claim 2wherein: the flowpath passes from the passageway legs in the first piecethrough an annular channel in the first piece and to the plenum.
 4. Theseal system of claim 2 wherein: the passageway legs are first passagewaylegs, the flowpath passing from the first passageway legs and throughrespective associated second passageway legs in the first piece and tothe plenum.
 5. The seal system of claim 4 wherein: the second passagewaylegs have respective spiral surface enhancements.
 6. The seal system ofclaim 4 wherein: the second passageway legs are threaded.
 7. The sealsystem of claim 1 wherein: the seal is a carbon seal.
 8. The seal systemof claim 1 wherein: the seat is steel; and the seat and seal are fullannular.
 9. A gas turbine engine including the seal system of claim 1wherein: the second member is a shaft.
 10. The gas turbine engine ofclaim 1 wherein the seal system further comprises: an oil sourcepositioned to introduce oil to the passageway legs.
 11. A method forusing the seal system of claim 1, the method comprising: relativelyrotating the second member to the first member about the axis; and therotation centrifugally driving a flow of oil along the flowpath to coolthe seat face.
 12. The method of claim 11 further comprising: sprayingthe oil from a nozzle.
 13. A seal system comprising: a first membercomprising a seal with a seal face; and a second member comprising aseat with a seat face and a plurality of cooling passageways, wherein:the second member is rotatable about an axis relative to the firstmember; the seal face and the seat face are in sliding sealingengagement; and the cooling passageways have respective surfaceenhancements.
 14. The seal system of claim 13, wherein: each coolingpassageway surface enhancement is at least one spiral.
 15. The sealsystem of claim 14, wherein: each cooling passageway surface enhancementis a thread.
 16. The seal system of claim 13 wherein: the second memberfurther has a collection channel; the second member further has aplurality of feed passageways, each feed passageway coupling anassociated said cooling passageway to the collection channel.
 17. Theseal system of claim 16 wherein: each said feed passageway is positionedat an oblique angle relative to both the collection channel and theassociated cooling passageway; the second member is coupled to andconfigured to rotate with a rotatable shaft; the first member isconfigured to remain stationary while the second member rotates with therotatable shaft; the seal system includes between 10 and 100 coolingpassageways and between 10 and 100 feed passageways; a distance betweenan outermost edge of the grooves of the threaded passageway and the seatface is between 0.76 mm and 6.35 mm; a an angle formed between a centeraxis of each cooling passageway and the seat face is greater than zero;the seal system is a dry face seal; and the feed passageways and coolingpassageways are configured to provide cooling fluid such that thecooling fluid remains separate from an interface where the seal face andthe seat face are in sliding engagement.
 18. A gas turbine enginecomprising: an engine case, a fan, a compressor section, a turbinesection, and a rotating shaft; and the seal system of claim 13positioned within the compressor section of the gas turbine engine.